Microsoft's DNS server servers are apparently failing to respond to requests, returning "no record" errors. This means that you can't access sites like Hotmail.com, MSN.com, and Live.com. It's unknown how widespread this outage is at this time. Currently msn.com, live.com, hotmail.com, and outlook.com, azure.com, and microsoft.com are all known to be impacted. It's very probable that all Microsoft domains are currently unavailable.

Do a search for "dns microsoft" on Twitter, and you'll find many people reporting the same thing. Could this be a load issue related to the Xbox One launch? Or are their DNS servers being actively DDoS (Distributed Denial of Service) attacked?

For those who are not experiencing an issue, it could be because the provider you're using is caching the results. DNS records utilize a "Time to Live" (TTL), and only ask the master server for an update once that TTL has expired.